Not applicable.
This invention relates to a switch lockout mechanism for a power tool, and, more particularly, to a mechanism that locks the power switch in an xe2x80x9coffxe2x80x9d position and requires an operator to actuate a separate lever to orient the switch to its xe2x80x9conxe2x80x9d position.
Power tools, such as circular saws, typically have a handle molded into the body of the tool. Such a handle is grasped by the power tool operator to guide and propel the tool through the workpiece. Usually, in a circular saw, there is a rear handle and a forward handle. The rear handle oftentimes resembles a pistol grip, and extends upwardly and forwardly. The handle is separated from the body of the saw so that the operator can easily grasp an elongated handle section that fits comfortably within the hand of the operator. This handle section typically extends in a direction that is generally parallel to and along the line of travel of the saw. As is apparent, it is extremely desirable to have the on/off switch for the saw located where it can be actuated by at least the index finger of the operator""s hand engaging the handle. Such an arrangement allows an operator to selectively start and stop the cutting operation of the saw while having his/her hand gripping the handle.
Many prior power tool constructions have a lockout mechanism also associated with the handle structure which holds the switch on the handle in a locked position and requires the operator to actuate the mechanism prior to turning the power tool to the xe2x80x9conxe2x80x9d position utilizing the switch. In particular, many of these prior structures require an operator to actuate a separate button or lever with his/her thumb prior to or simultaneously with actuation of the switch by the index finger of the operator""s hand gripping the handle.
Prior lockout mechanisms or latches typically are of two main types, a pivoting type and a sliding type. In a pivot-type arrangement the latch is pivotally mounted within the handle structure about an axis which is transverse or perpendicular to the elongated direction of the handle. In the case of a circular saw, the latch is pivotally mounted about an axis that is parallel to the axis of rotation of the saw blade. These latches operate by pivoting between an engaged position wherein the handle switch contacts the latch member and is prevented from movement to its xe2x80x9conxe2x80x9d position, and a disengaged position wherein the operator is allowed to actuate the switch to the xe2x80x9conxe2x80x9d position. Examples of these transverse pivotal lockout mechanisms can be found in U.S. Pat. No. 3,873,796 and U.S. Pat. No. 5,577,600. In each of these references, the latch mechanism is actuated by a button located on the top surface of the handle. In particular, they require either the pushing of the button or the rotating of the button rearwardly to allow actuation of the switch. These structures are disadvantageous for various reasons. In particular, the location of the lockout mechanism button on the top surface of the handle requires the positioning of the thumb in an awkward position. More specifically, it is natural when gripping a handle for the thumb to be along the side of the handle with the cross section of the handle received between the thumb and index finger. As is apparent, to actuate the mechanisms in these references, the thumb must first be positioned on the top of the handle, thus resulting in a less secure grip on the handle. Such loose gripping can result in misalignment of the saw during its initial cutting actions. Still further, in these prior references, for the thumb to reach the normal gripping position on the side of the handle, the thumb must slide off the button and over the side of the handle. The friction associated with the thumb passing over the top surface of the handle and the awkward sideward movement of the thumb can result in operator discomfort during the initial cutting action of the saw.
A still further disadvantage of these references is the location of the lockout mechanism at the same general location of or behind the location of the on/off switch with respect to the longitudinal axis of the handle. More specifically, when a person typically grabs a handle, the tendency is for the thumb to be forward of the index and middle fingers. To actuate the lockout mechanism buttons of these references, the thumb must be moved rearwardly to push the actuating button, thus presenting a potential awkward position for the saw operator, and, further, possibly resulting in unnecessary reorientation of the thumb along the side of the handle to the normal gripping position.
These references suffer from a further disadvantage in that they do not provide a xe2x80x9ctriggerxe2x80x9d feel or structure for saw operation. More specifically, in each of these references, the trigger mechanism is pivotally mounted at a location far down the handle from the normal positioning of the index finger of the operator. The pivoting arc of such structures is relatively great and results in the trigger lever or button extending a fair distance longitudinally within the handle structure. As is apparent, to have a true xe2x80x9ctriggerxe2x80x9d type feel to an actuating switch, and to decrease the space necessary for the switch, it may be desirable to have the pivot point for the switch located at a location adjacent the index finger of the operator""s hand as it grips the handle. Thus, the rotation of a switch is truly of a xe2x80x9ctriggerxe2x80x9d nature if the pivot point is located adjacent the top of the switch and the lower end of the switch rotates inwardly toward the handle. The large trigger structures of the above references also may result in some instability and finger fatigue in operating the structure. More specifically, because the trigger structure is not confined by a guard but extends along the length of the handle, it may be difficult for an operator to align his or her fingers with the trigger for actuation thereof.
The second type of lockout mechanism includes a latch member which, when actuated, slides within the handle housing to allow actuation of the on/off switch by the operator. An example of this type of sliding latch member is disclosed in U.S. Pat. No. 5,638,945. These sliding lockout mechanisms are oftentimes relatively complicated and do not allow ergonomic positioning of the thumb during the beginning power tool operation. More specifically, the lockout structure of the above patent, again, has the actuating button positioned on the top surface of a handle housing and at a location that is above the actuating switch for the power tool. Thus, an operator, to use the power tool, is required to position his or her thumb on the top of the handle instead of along the side, and to push the lockout mechanism button forward on the upper surface while pushing upward on the switch, and thereafter to slide the thumb of the hand positioned on the handle to the side of the handle to the normal comfortable gripping position. As with the pivoting latch mechanisms discussed above, this sliding-type mechanism is highly disadvantageous because it requires the operator to utilize significant effort to reposition his or her thumb in a normal gripping operation, and also has the sliding actuating switch or button located generally at the same location as the on/off switch along a longitudinal axis of the handle which is typically not a normal position for a user""s thumb of the hand gripping the handle. An additional disadvantage of sliding mechanisms is that they are oftentimes subject to contamination by dirt or grease, which affects their operations. In particular, sliding mechanisms often have grooves and sliding surfaces which can become fouled easily.
Prior art lockout mechanisms are also oftentimes subject to substantial forces as an operator attempts to actuate the power switch with the lockout mechanism in its locked position. Sometimes, such prior art mechanisms will give way and actually allow actuation of the power switch, without the operator first utilizing the button or other structure to disengage the lockout mechanism.
Therefore, a lockout mechanism is needed which will overcome the problems with the prior art lockout mechanisms discussed above.
An object of the present invention is to provide a lockout mechanism for a power tool wherein the force vector of the switch of the lockout mechanism is aligned at a predetermined location to help prevent inadvertent bypassing of the lockout mechanism by strong pressure on the switch.
A further object of the present invention is to provide a lockout mechanism for a power tool, wherein the actuating lever of the lockout mechanism is positioned at a location that is ergonomically advantageous for the operator and that allows easy transition from actuation of the lockout mechanism to the normal gripping operation of the power tool.
A still further object of the present invention is to provide a lockout mechanism for a power tool wherein the lockout mechanism pivots in the rotational direction of the normal thumb action of the user.
A still further object of the present invention is to provide a lockout mechanism with an actuating lever which is oriented such that the thumb can be moved easily downward over the surface of the actuating lever to its normal gripping position.
A still further aspect of the present invention is to provide a lockout mechanism that can accommodate a xe2x80x9ctriggerxe2x80x9d type power switch which is pivotally mounted forwardly on the handle.
Yet another object of the present invention is to provide a lockout mechanism that is resistant to contamination and fouling.
Accordingly, the present invention provides for a power tool, including a hollow housing defining a handle with an external wall. A motor is disposed in the housing, and a switch is pivotally mounted in the handle about a first axis for actuating the motor. The switch also has a first locking abutment. A latch is located adjacent the switch and is pivotally mounted in the handle about a second axis generally parallel to the first axis for movement back and forth between an engaged and a disengaged position. The latch has a second abutment for engaging the first abutment and preventing the switch from being actuated. The switch when pivoted to engage the first and second abutments applies a force vector generally intersecting the second axis. The latch of the lockout mechanism is pivoted to a disengaged position in a rotational direction that is the same as the normal downward pivoting action of the user""s thumb.
The present invention includes the structure as described above, wherein the latch is a generally L-shaped leg with first and second segments connected by a knee. The knee forms the pivot point to the latch. Such invention further includes an actuating lever extending transverse to the leg and disposed on the first segment. The first segment extends in a direction forward of the second axis.
The present invention also provides for the latch of the lockout mechanism to have a surface for engagement of the thumb of the user, with the surface sloping downwardly in the direction of the movement of the thumb of the user when moving the latch from an engaged to a disengaged position.
Additional objects, advantages and novel features of the invention will be set forth in part in a description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.